Imaging control apparatus for capturing tomogram of fundus, imaging apparatus, imaging control method, program, and storage medium

ABSTRACT

An imaging control apparatus which controls an imaging unit configured to capture a tomogram of the fundus of a target eye includes an acquisition unit configured to acquire information representing the direction of a fundus movement of the target eye, an analysis unit configured to analyze the direction of the fundus movement based on the information acquired by the acquisition unit, and a control unit configured to control the imaging unit so as to align the direction of imaging of the imaging unit with the direction of the fundus movement based on the analysis result of the analysis unit.

CROSS REFERENCE

This application is a continuation of patent application Ser. No.12/759,622, filed Apr. 13, 2010, which is a continuation ofInternational Application No. PCT/JP2009/004360, filed Sep. 3, 2009,which claims priority to Japanese Patent Application No. 2008-271439,filed Oct. 21, 2008, all of which are hereby incorporated by referenceherein in their entireties.

TECHNICAL FIELD

The present invention relates to an imaging control apparatus, imagingapparatus, imaging control method, program, and storage medium.

BACKGROUND ART

Eye examinations are widely made for the purpose of early diagnosis oflife-related diseases or various diseases that are leading causes ofblindness. In the examinations and the like, it is necessary to finddiseases all over the eye. For this reason, an examination using animage (to be referred to as a broad image hereinafter) in a broaderrange of an eye is essential. A broad image is obtained using, forexample, a fundus camera or an SLO (Scanning Laser Ophthalmoscope).

On the other hand, an eye tomogram acquisition apparatus of an OCT(Optical Coherence Tomography) or the like can quantify a disease statebased on an objective measure and is therefore expected to be useful formore reliably diagnosing diseases. In a general OCT, an operator decidesthe tomogram imaging parameters (for example, target part, imagingrange, precision level, scanning method, and the like), and images andanalyzes only a local eye region based on the imaging parameters.

As a technique of assisting operator's tomographic imaging, for example,patent reference 1 discloses a technique concerning a user interface fordesignating the tomographic imaging range of an OCT on a broad imageobtained by a fundus camera. Patent reference 2 discloses a techniqueconcerning a user interface for designating the tomographic imagingrange of an OCT on a broad image obtained by an SLO.

According to patent reference 1 or 2, the imaging parameters can be setrelatively easily because it is possible to decide the tomographicimaging range while referring to the state of a broad fundus image.

However, the human eye is constantly in an unconscious feeble motioncalled a small involuntary eye movement even when gazing at a fixedpoint. The small involuntary eye movement is known to mainly containthree components (feeble motion components) (see FIG. 4).

(1) Tremor: a frequency component of 30 to 100 Hz at a visual angle ofabout 50°.

(2) Flick: a step- or pulse-like movement which occurs withoutperiodicity (at an interval of about 0.03 to 5 sec) at a visual angle ofabout 20°.

(3) Drift: a slow movement which exists between flicks at a visual angleof about 10′.

During the measurement processing time of the OCT, a measurement lightbeam needs to accurately strike a measurement part. Actually, it isdifficult to continuously accurately apply a measurement light beam to ameasurement part because of, for example, the small involuntary eyemovement of the target eye.

Each of patent references 3 and 4 discloses an apparatus which includesa tracking means for moving the irradiation position of a measurementlight beam onto a measurement part in real time in correspondence with asmall involuntary eye movement.

PRIOR ART REFERENCES

Patent References

Patent reference 1: Japanese Patent Laid-Open No. 2007-117714

Patent reference 2: Japanese Patent Laid-Open No. 2008-029467

Patent reference 3: Japanese Patent Laid-Open No. 6-503733

Patent reference 4: Japanese Patent Laid-Open No. 7-155299

Non-Patent References

Non-patent reference 1: Koji Imao et al.: “Estimation of MotionDirection from Motion Blur in Image Sequence”, Proceedings of the IEICEGeneral Conference, Vol. 1997 No. 2

Non-patent reference 2: Krahmer, F. et al.: “Blind Image Deconvolution:Motion Blur Estimation”, 2006

Non-patent reference 3: Moghaddam, M. E. et al.: “Linear motion blurparameter estimation in noisy images using fuzzy sets and powerspectrum”, EURASIP Journal on Advances in Signal Processing, 2007

DISCLOSURE OF INVENTION

Problems that the Invention is to Solve

When manually designating imaging parameters for tomographic imaging,the state of a small involuntary eye movement of the target eyeimmediately before imaging may be unknown, and the influence of a smallinvoluntary eye movement may be suppressed by shortening the measurementtime. In this case, the number of measurement points (sampling points)is also decreased. It is therefore not easy to appropriately set suchimaging parameters that minimize the influence of a small involuntaryeye movement.

Use of the technique of patent reference 3 or 4 allows to suppress theinfluence of a small involuntary eye movement by correcting OCT imagingwhile detecting the small involuntary eye movement. In this case,imaging is done based on a preset traversal scan speed and direction.Hence, the traversal scan speed and direction for imaging are not set inaccordance with the characteristics of the small involuntary eyemovement of each target eye upon imaging. An apparatus having thetracking function becomes complex because it needs to emit themeasurement beam and the tracking beam simultaneously.

Means of Solving the Problems

The present invention has been made in consideration of theabove-described problems, and has as its object to provide an imagingcontrol technique capable of suppressing the influence of an eyemovement in tomographic fundus imaging.

According to one aspect of the present invention, there is provided animaging control apparatus which controls an imaging unit adapted tocapture a tomogram of a fundus of a target eye, comprising:

an acquisition unit adapted to acquire information representing adirection of a fundus movement of the target eye;

an analysis unit adapted to analyze the direction of the fundus movementbased on the information acquired by the acquisition unit; and

a control unit adapted to control the imaging unit so as to align adirection of imaging of the imaging unit with the direction of thefundus movement based on an analysis result of the analysis unit.

Effects of the Invention

According to the present invention, it is possible to provide an imagingcontrol technique capable of suppressing the influence of an eyemovement in tomographic fundus imaging.

Further features and advantages of the present invention will becomeapparent from the following description with reference to theaccompanying drawings. Note that the same reference numerals denote thesame or similar parts throughout the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention and,together with the description, serve to explain the principles of theinvention.

FIG. 1 is a block diagram showing the arrangement of a control apparatus1 of a tomographic fundus imaging apparatus according to the firstembodiment;

FIG. 2 is a block diagram showing the functional arrangement of thecontrol apparatus 1 of the tomographic fundus imaging apparatusaccording to the first embodiment;

FIG. 3 is a flowchart illustrating the processing procedure of thecontrol apparatus 1 of the tomographic fundus imaging apparatusaccording to the first embodiment;

FIG. 4 is a view showing three components of a small involuntary eyemovement that is a fundus movement;

FIG. 5 is a block diagram showing the functional arrangement of a broadimaging apparatus 2 according to the first embodiment;

FIG. 6 is a block diagram showing the functional arrangement of atomographic imaging apparatus 3 according to the first embodiment;

FIG. 7 is a view for explaining a scan movement in tomographic imaging;

FIG. 8 is a view showing an example of displaying a broad image and atomogram acquisition range together according to the first embodiment;

FIG. 9 is a flowchart illustrating the processing procedure of fundusmovement analysis according to the first embodiment;

FIG. 10 is a view showing an example of a broad image according to thefirst embodiment;

FIG. 11 is a flowchart illustrating the processing procedure of imagingparameter setting according to the first embodiment;

FIG. 12 is a view showing the relationship between a fundus movementdirection and a traversal scan direction according to the firstembodiment;

FIG. 13 is a flowchart illustrating the processing procedure of acontrol apparatus 1 of a tomographic fundus imaging apparatus accordingto the fourth embodiment;

FIG. 14 is a graph for explaining the parameters of a Point SpreadFunction to model a motion blur according to the first embodiment; and

FIG. 15 is a graph showing an example of the probability distribution offlicks according to the third embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will now be described indetail with reference to the accompanying drawings. Note that theconstituent elements described in the embodiments are merely examples.The technical scope of the present invention is determined by the scopeof claims and is not limited by the following individual embodiments.

First Embodiment

The arrangement of the embodiment will be explained first. FIG. 1 is ablock diagram schematically showing the apparatus arrangement of adiagnostic system according to an embodiment of the present invention. Atomographic fundus imaging apparatus for capturing a tomogram of thefundus of a target eye includes a control apparatus 1. The controlapparatus 1 includes a central processing unit (CPU) 100, main memory101, magnetic disk 102, control program 103, display memory 104, monitor105, mouse 106, keyboard 107, and common bus 108.

The central processing unit (CPU) 100 mainly controls the operation ofeach constituent element of the control apparatus 1 (imaging controlapparatus). The main memory 101 can store an apparatus control programand function as a work area for program execution. The magnetic disk 102stores an operating system (OS), the device drives of peripheraldevices, the control program 103 (to be also simply referred to as a“program” hereinafter) to be used to perform various kinds of processesto be described later, and the like. The display memory 104 cantemporarily store display data. The monitor 105 is, for example, a CRTmonitor or a liquid crystal monitor and displays an image based on datafrom the display memory 104. The mouse 106 and the keyboard 107 are usedfor pointing input and input of characters and the like by the user,respectively. The common bus 108 connects the above-describedconstituent elements to each other.

As shown in FIG. 1, the control apparatus 1 of the tomographic fundusimaging apparatus (imaging apparatus) is connected to a broad imagingapparatus 2 and a tomographic imaging apparatus 3 via a local areanetwork (LAN) 4 such as Ethernet. Note that the devices may be connectedvia an external interface such as a USB or IEEE1394.

The broad imaging apparatus 2 captures a broad image of an eye andincludes, for example, a fundus camera or an SLO (Scanning LaserOphthalmoscope).

FIG. 5 illustrates the functional arrangement of the broad imagingapparatus 2 formed from an SLO. As shown in FIG. 5, to capture a broadeye image, the broad imaging apparatus 2 controls a polygon mirror 520and a galvano mirror 530 via a scan driving mechanism 510. Alight-receiving element 540 formed from, for example, a CCD receives thereflected light of a weak laser beam emitted from an imaging lightsource 500, thereby capturing g a broad eye image. Note that the devicearrangement and driving mechanism control of the SLO are described indetail in patent reference 2. In this embodiment, an example will bedescribed in which an image from a fundus camera serving as the broadimaging apparatus is used. The device arrangement and driving mechanismcontrol of the fundus camera are described in detail in patent reference1.

The tomographic imaging apparatus 3 captures a tomogram of an eye andincludes, for example, an OCT (Optical Coherence Tomography) of timedomain scheme or an OCT of Fourier domain scheme. FIG. 6 illustrates thefunctional arrangement of the tomographic imaging apparatus 3 formedfrom an OCT of time domain scheme. The tomographic imaging apparatus 3receives parameters for designating imaging contents from the controlapparatus 1 of the tomographic fundus imaging apparatus and executestomographic imaging using the received parameters. The obtained tomogramis output to the control apparatus 1 of the tomographic fundus imagingapparatus.

The parameters for designating imaging contents designate a scanningmethod including a tomogram acquisition part and position, the spatialrange of a tomogram, a precision level such as a scan line (A scan)interval, a traversal scan order, a scan direction, and a scan speed.FIG. 7 shows an example of a fundus image 701 obtained from the broadimaging apparatus 2 and an example of a retinal tomogram 702 obtainedfrom the tomographic imaging apparatus 3. Reference numeral 701 aindicates a position of the tomogram 702. In the example of FIG. 7, thetomogram 702 is formed from a plurality of scan lines (also called Ascans) 703 that scan in the depth direction of the retina. The scanlines travel on the retina to form one tomogram. Reference numerals 704and 704 a indicate traveling of the scan lines. The traveling is alsocalled traversal scan or main scan. When continuously capturingtomograms, the imaging traveling is represented by 705 or 705 a. Thistraveling is also called sub-scan.

The tomographic imaging apparatus 3 controls a reference mirror drivingmechanism 601 and a galvano mirror driving mechanism 603 in accordancewith the parameters to drive a reference mirror 602 and a galvano mirror604. A light-receiving element 605 formed from, for example, a CCDreceives the reflected light of light emitted from a low-coherence lightsource 600, thereby capturing an eye tomogram. Note that if thetomographic imaging apparatus 3 is formed from an OCT of Fourier domainscheme, only the galvano mirror 604 is controlled. Note that the devicearrangement and driving mechanism control of the OCT are described indetail in patent reference 1 or 2.

The functional arrangement of the control apparatus 1 of the tomographicfundus imaging apparatus will be described next with reference to FIG.2. FIG. 2 is a functional block diagram of the control apparatus 1 ofthe tomographic fundus imaging apparatus according to the embodiment. Asshown in FIG. 2, the control apparatus 1 of the tomographic fundusimaging apparatus includes a target eye information acquisition unit210, broad image acquisition unit 220, tomogram acquisition unit 230,instruction acquisition unit 240, data storage unit 250, display unit260, and tomogram acquisition parameter processing unit 270.

(Target Eye Information Acquisition Unit 210)

The target eye information acquisition unit 210 externally acquiresinformation to identify a target eye. Information to identify a targeteye is, for example, an identification number assigned to each targeteye. Otherwise, the identification number of the target eye and anidentifier representing whether the target eye is a right eye or lefteye may be combined and used as the information to identify a targeteye. The information also contains ecological information such as theage and medical record of the patient.

The operator inputs the information to identify the target eye. Notethat when the tomographic imaging apparatus 3 holds the information toidentify the target eye, the information may be acquired from thetomographic imaging apparatus 3 together with a tomogram. Based on theinformation to identify the target eye, the target eye informationacquisition unit 210 also acquires information about the target eye heldin the magnetic disk 102.

(Instruction Acquisition Unit 240)

The instruction acquisition unit 240 functions as a setting means forreceiving imaging parameter settings to obtain a fundus tomogram. Theinstruction acquisition unit 240 acquires a process instruction that theoperator inputs using the mouse 106 or the keyboard 107. For example,the instruction acquisition unit 240 acquires imaging parameters such asa fundus tomogram imaging position and imaging range to obtain a fundustomogram. Alternatively, the instruction acquisition unit 240 acquiresan imaging start instruction, initial parameters of tomogram acquisitionparameters, an instruction to designate whether to store a capturedtomogram, an instruction of a storage location, and the like. Theinstruction acquisition unit 240 transmits the contents of acquiredinstructions to the broad image acquisition unit 220, tomogramacquisition unit 230, data storage unit 250, display unit 260, andtomogram acquisition parameter processing unit 270 as needed.

(Broad Image Acquisition Unit 220)

Based on an instruction acquired by the instruction acquisition unit240, the broad image acquisition unit 220 requests the broad imagingapparatus 2 to capture and transmit a broad image and acquires a broadeye image transmitted from the broad imaging apparatus 2. The broadimage acquisition unit 220 transmits the acquired broad image to thetomogram acquisition parameter processing unit 270, display unit 260,and data storage unit 250.

(Tomogram Acquisition Unit 230)

Based on an instruction acquired by the instruction acquisition unit240, the tomogram acquisition unit 230 transmits a tomographic imagingrequest to the tomographic imaging apparatus 3 together with parametersset by a tomogram acquisition parameter setting unit 272 to designateimaging contents. The tomogram acquisition unit 230 then acquires atomogram transmitted from the tomographic imaging apparatus 3. Thetomogram acquisition unit 230 transmits the acquired tomogram to thedisplay unit 260 and the data storage unit 250.

(Tomogram Acquisition Parameter Processing Unit 270)

The tomogram acquisition parameter processing unit 270 includes a fundusmovement analysis unit 271 and the tomogram acquisition parametersetting unit 272. Imaging parameters set by the tomogram acquisitionparameter processing unit 270 to designate imaging contents designate ascanning method including a tomogram acquisition part and position, thespatial range of a tomogram, a scan line interval, a scan order, a scanspeed, and a scan direction.

The fundus movement analysis unit 271 analyzes the broad image acquiredby the broad image acquisition unit 220 and calculates information abouta small involuntary eye movement (the direction of drift, the movingrange of drift and tremors, and the interval and instant of flicks). Thefundus movement analysis unit 271 transmits the analysis result to thetomogram acquisition parameter setting unit 272, display unit 260, anddata storage unit 250. Note that detailed contents of processing ofanalyzing the fundus movement will be described later more specifically.In this embodiment, an example will be explained in which fundusmovement information is acquired by analyzing a broad fundus image.However, the method of obtaining fundus movement information is notlimited to this. For example, a fundus movement may be estimated byanalyzing an image obtained by imaging the anterior segment (cornea,pupil, and iris). Alternatively, a fundus movement may be estimatedusing an eye movement detection method known for an eye-gaze inputapparatus.

Based on the target eye information acquired by the target eyeinformation acquisition unit 210, the instruction information acquiredby the instruction acquisition unit 240, and the fundus movementinformation obtained from the fundus movement analysis unit 271, thetomogram acquisition parameter setting unit 272 sets parameters(tomographic imaging parameters) associated with tomogram acquisition soas to minimize the influence of a fundus movement (small involuntary eyemovement) on an obtained image. Note that detailed contents ofprocessing of setting the tomographic imaging parameters based on theresult from the fundus movement analysis unit 271 will be describedlater more specifically.

The tomogram acquisition parameter processing unit 270 transmits the setimaging parameters to the tomogram acquisition unit 230, display unit260, and data storage unit 250.

(Data Storage Unit 250)

The data storage unit 250 stores various kinds of input information inthe magnetic disk 102 in association with each other as the data of apatient. More specifically, the data storage unit 250 stores the targeteye information input from the target eye information acquisition unit210, the broad image input from the broad image acquisition unit 220,the tomographic imaging parameters input from the tomogram acquisitionparameter processing unit 270, and the tomogram input from the tomogramacquisition unit 230. The data may be stored in an external server (notshown). In this case, the data storage unit 250 transmits the data tothe external server.

(Display Unit 260)

The display unit 260 displays, on the monitor 105, the broad imageacquired by the broad image acquisition unit 220 or the tomogramobtained by the tomogram acquisition unit 230. The display unit 260 alsodisplays the tomographic imaging parameters set by the tomogramacquisition parameter processing unit 270. If no tomogram can beacquired, information representing it is displayed. A broad fundus imagemay be displayed together to confirm the traversal scan order, scandirection, scan speed, and imaging position and range.

A detailed processing procedure executed by the control apparatus 1 ofthe tomographic fundus imaging apparatus according to this embodimentwill be described next with reference to FIG. 3. Note that the functionsof the units of the control apparatus 1 according to this embodiment areimplemented by causing the CPU 100 to execute a program for implementingthe functions of the units and control the overall computer. Prior tothe processing to be explained below, program codes complying with theflowchart are already loaded from, for example, the magnetic disk 102 tothe main memory 101.

(Process in Step S310)

In step S310, the instruction acquisition unit 240 acquires imaginginstruction information for the fundus of a target eye. The instructionacquisition unit externally acquires, as imaging instructions, forexample, the designations of the part, position, and imaging range onthe fundus of the broad image or tomogram acquisition target. Theoperator inputs these instructions via the mouse 106 or the keyboard107. The obtained instructions are transmitted to the broad imageacquisition unit 220, tomogram acquisition parameter processing unit270, and data storage unit 250.

(Process in Step S320)

In step S320, the broad image acquisition unit 220 requests the broadimaging apparatus 2 to capture and transmit a broad image and acquires abroad eye image transmitted from the broad imaging apparatus 2. Thebroad image acquisition unit 220 transmits the acquired broad image tothe fundus movement analysis unit 271, display unit 260, and datastorage unit 250.

In step S320, details of settings concerning parameters (the number ofimages and the shutter speed) of broad image acquisition will bedescribed later.

(Process in Step S330)

In step S330, the fundus movement analysis unit 271 performs imageprocessing of the broad image acquired in step S320 and detectsinformation about a fundus movement. The fundus movement analysis unit271 of this embodiment detects, as the fundus movement, the momentum anddirection of the involuntary small eye movement. The momentum anddirection of the involuntary small eye movement are detected byanalyzing a motion blur of the broad image acquired in step S320 ordetecting the optical flow of the broad image. Detailed contents of eachprocessing will be described later more specifically.

(Process in Step S340)

In step S340, the tomogram acquisition parameter setting unit 272 setsthe direction and speed of traversal scan for tomogram acquisition basedon the fundus movement information detected in step S330. Based on theinstruction information acquired in step 310, the tomogram acquisitionparameter setting unit 272 also sets parameters to designate thecontents of tomographic imaging. Examples of the parameters are theposition and range of tomographic imaging on the fundus. The result istransmitted to the tomogram acquisition unit 230, display unit 260, anddata storage unit 250. To reduce the influence of a small involuntaryeye movement on the tomographic imaging, the tomographic imaging time isset based on the moving amount of the small involuntary eye movement,and the traversal scan direction of a tomogram is set based on themoving direction information of the small involuntary eye movement.Detailed contents of each setting processing will be described latermore specifically.

(Process in Step S350)

In step S350, the tomogram acquisition unit 230 acquires a tomogram fromthe tomographic imaging apparatus 3 based on the tomographic imagingparameters set in step S340. More specifically, the tomogram acquisitionunit 230 transmits a tomographic imaging request to the tomographicimaging apparatus 3 together with the parameters to designate theimaging contents. The tomogram acquisition unit 230 then acquires atomogram transmitted from the tomographic imaging apparatus 3. Thetomogram acquisition unit 230 transmits the acquired tomogram to thedisplay unit 260 and the data storage unit 250. Note that if imaging ata plurality of positions is instructed in step S340, the tomogramacquisition unit 230 transmits imaging requests using the respectiveimaging parameters to the tomographic imaging apparatus 3 to executeimaging a plurality of number of times.

(Process in Step S360)

In step S360, the display unit 260 displays, the monitor 105, thetomogram obtained in step S350. At this time, the broad image and thetomogram acquisition range on it may be presented together for thepurpose of, for example, confirming the imaging part. In addition, thetomographic imaging parameters may be displayed together. FIG. 8 shows adisplay example. In this example, a broad image 801 and a tomogramacquisition range 801 a are displayed on the left side, and an acquiredtomogram 802 is displayed on the right side. The tomogram acquisitionrange 801 a also indicates the traversal scan direction and the intervalof the imaging positions of a plurality of tomograms.

(Process in Step S370)

In step S370, the data storage unit 250 stores, in the magnetic disk102, the various kinds of information input in the above-described stepsin association with each other as the data of a patient. Morespecifically, the data storage unit 250 stores the imaging instructioninformation acquired in step S310, the broad image obtained in stepS320, the fundus movement analysis result obtained in step S330, thetomographic imaging parameters obtained in step S340, and the tomogramobtained in step S3350. All the data need not always be stored, as amatter of course.

Note that the data may be stored in an external server (not shown). Inthis case, the data storage unit 250 transmits the data to the externalserver.

(Fundus Movement Analysis Processing)

The procedure of fundus movement analysis processing executed in stepS330 will be described next with reference to FIG. 9. In thisembodiment, a fundus movement is estimated using the property that anobject movement at the time of imaging leads to a blur or defocus(motion blur) of a captured image. To do this, the momentum anddirection of a fundus movement are estimated using two broad images atdifferent shutter speeds.

In this embodiment, a PSF (Point Spread Function) is used as the imagegeneration model of a defocus (motion blur) in a broad image B caused bya fundus movement to estimate the PSF parameters, thereby estimating themomentum and direction of the motion blur.

An image g(x,y) containing a motion blur is modeled as the convolutionintegral of a blur-free image f(x,y) and a PSF p(x,y).

g(x,y)=f(x,y)*p(x,y)

The fundus movement includes not only a movement in one direction butalso directional movements (drift and flicks) and also non-directionalmovements (tremors). Hence, the defocus in the broad image B can beexpressed in a plurality of directions (see FIG. 12).

In this embodiment, the PSF of a motion blur is approximated by thefollowing expression (see FIG. 14). FIG. 14 is a graph for explainingthe parameters of the Point Spread Function to model a motion blur.

$\begin{matrix}{{p\left( {x,{y;r},l,\theta} \right)} = \left\{ {{\begin{matrix}{\frac{1}{\pi \left( {l^{2} + r^{2}} \right)};} & {{{\left( \frac{x^{\prime}}{l} \right)^{2} + \left( \frac{y^{\prime}}{l} \right)^{2}} \leq 1},} \\{0;} & {otherwise}\end{matrix}\mspace{79mu} {for}\mspace{14mu} \begin{pmatrix}x^{\prime} \\y^{\prime}\end{pmatrix}} = {\begin{pmatrix}{\cos \; \theta} & {\sin \; \theta} \\{{- \sin}\; \theta} & {\cos \; \theta}\end{pmatrix}\begin{pmatrix}x \\y\end{pmatrix}}} \right.} & \left\lbrack {{Mathematical}\mspace{14mu} 1} \right\rbrack\end{matrix}$

where x and y are the positions from a pixel of interest, r is themagnitude of the motion blur in a direction in which the moving amountis small, and l and θ are the magnitude and direction of the motion blurin a direction in which the moving amount is large. In this embodiment,r, l, and θ are used as the PSF parameters.

To estimate the parameters r, l, and θ of the PSF, an image without amotion blur and an image containing a motion blur are obtained. Motionblur images are generated from the image without a motion blur usingvarious values of the parameters r, l, and θ. The generated motion blurimages are searched for an image most similar to the captured motionblur image. The PSF parameters of the generated similar image are usedas the PSF parameters of the captured motion blur image.

(Process in Step S910)

In step S910, a fundus image at a high shutter speed is acquired fromthe broad imaging apparatus 2 via the broad image acquisition unit 220.To avoid a blur caused by a flick and drift having a large momentum outof the small involuntary eye movement, the shutter speed is set in, forexample, seconds. This shutter speed is not sufficient for avoiding theinfluence of tremors because a tremor has a frequency of 30 to 100 Hz,as described above. However, the momentum of a tremor itself is smallerthan those of the flicks and drift. Hence, tremors are neglected in thisembodiment. A higher shutter speed may be set to avoid the influence oftremors. Any shutter speed capable of avoiding flicks and drift isusable even if it is not in seconds as will be described here, and theembodiment is not limited to this. Reference numeral 1010 in FIG. 10represents an example of a broad image at a high shutter speed. Thebroad image captured at a high shutter speed will be referred to as a“broad image A” hereinafter.

(Process in Step S920)

In step S920, a fundus image at a low shutter speed is acquired from thebroad imaging apparatus 2 via the broad image acquisition unit 220. Toobtain a broad image containing the momentum of a small involuntary eyemovement as a blur, the shutter speed is set in, for example, seconds.Regarding the small involuntary eye movement, the fundus sometimes movesin a moving width of 0.1 to 0.5 mm per sec. When capturing an image of1024×1024 pixels in a 15 mm×15 mm fundus region, the fundus moves by 7to 35 pixels on the image at the shutter speed in seconds and causesdefocus in that width. The broad image size, imaging region, and shutterspeed are not limited to the above-described examples, as a matter ofcourse. Any values different from those of the embodiment can be adoptedas far as the fundus movement appears as a blur in the captured image.Reference numeral 1020 in FIG. 10 represents an example of a broad imageat a low shutter speed. The broad image captured at a low shutter speedwill be referred to as the “broad image B” hereinafter.

(Process in Step S930)

In step S930, the broad image A free from (or with a few) motion blursis defined as f(x,y), and convolution processing is performed based onthe PSF p(x,y) using various parameters r, l, and θ, as described above.The motion blur images g(x,y) of the respective parameters r, l, and θare thus generated.

g(x,y)=f(x,y)*p(x,y)

For the parameter θ, the slope is important but no direction informationis used. Hence, an image is generated within the range of π>θ>0.

In addition, an image is generated within the range ofm_(max)≧l≧r≧m_(min). The values m_(max) and m_(min) can be either valuesobtained from the instruction acquisition unit 240 or values stored inthe data storage unit 250 in advance.

Needless to say, the convolution processing need not always be executedfor the entire broad image A. The processing may be executed for apartial region of interest in the broad image A, for example, a regiondesignated by an operator instruction acquired by the instructionacquisition unit 240 or a region to be subjected to tomographic imaging.

(Process in Step S940)

In step S940, the PSF images of various parameters r, l, and θ generatedfrom the broad image A are compared with the broad image B, therebysearching for an image most similar to the broad image B.

In this embodiment, to measure the similarity, a description will bemade using an SSD (Sum of Square Differences).

$\begin{matrix}{{SSD} = {\frac{1}{N}{\sum\left( {{A(x)} - {B(x)}} \right)^{2}}}} & \left\lbrack {{Mathematical}\mspace{14mu} 2} \right\rbrack\end{matrix}$

The captured broad image B is searched for a portion (position x wherethe SSD is minimized) that is most similar to the reproduced motion blurimage in the region of interest.

While comparing with the generated PSF images of the parameters r, l,and θ, the minimum SSDs of the respective images are searched for aminimum SSD. The parameters r, l, and θ of the generated motion blurimage at this time are defined as the motion blur parameters.

In this embodiment, a fixed broad image capturing time will beexemplified for the descriptive convenience. However, the time may bechanged depending on the target eye information obtained from the targeteye information acquisition unit 210. For example, the amount of apatient's fundus movement is known to increase with advancing years. Formore accurate analysis, broad images may be captured in a plurality ofimaging times and analyzed.

In the above embodiment, the method of estimating the momentum anddirection of a fundus movement using PSFs having various parameters hasbeen described. However, the embodiment is not limited to this.

For example, Fourier transform of the equation

g(x,y)=f(x,y)*p(x,y) yields G(u,v)=F(u,v) P(U,V).

G(u,v) represents the Fourier transform of the broad image B; F(u,v);the Fourier transform of the broad image B; and p(x,y), the Fouriertransform of the PSF. P(U,V) is obtained from G(u,v) and F(u,v).

Additionally, p(x,y) can be obtained from P(U,V). The parameters r, l,and θ are thus obtained.

Alternatively, non-patent reference 1 or 2 presents a motion blurestimation method using a Point Spread Function in detail.

As a method capable of estimating motion blur parameters from one broadimage, a method of estimating the momentum and direction of a motionblur by analyzing the Fourier space of an image is presented innon-patent reference 3.

The process in step S330 is executed in the above-described way.

(Tomogram Acquisition Parameter Setting Processing)

The procedure of tomogram acquisition parameter setting processingexecuted in step S340 will be described next with reference to FIG. 11.

In step S340, the tomographic imaging time and the traversal scandirection of tomographic imaging are set based on the fundus movementestimation result obtained in step S330.

(Step S1110)

In step S1110, based on the fundus momentum estimation result obtainedin step S340, the tomographic imaging time is decided, and additionally,the traversal scan speed and the imaging range are set. When themomentum is large, a tomogram needs to be captured in a shorter time toreduce the influence on tomographic imaging. Conversely, when themomentum is small, its influence on tomographic imaging is expected tobe small, and a tomogram can be captured in a longer time.

The A scan acquisition capability speed of the tomographic imagingapparatus 3 is assumed to be 40,000 A Scan/sec for the descriptiveconvenience. To capture 128 tomograms each having a 512-pixel width in a6×4 mm region on a fundus surface (retina), an imagingtime=(512*128)/400000=1.64 sec is necessary. The size per pixel in thetraversal scan direction is 11.72 μm. In this case, the traversal scanspeed is 468 mm/sec with respect to the still fundus surface.

In this example, the interval between the continuously capturedtomograms is 31.5 μm if the fundus remains still. However, the intervalmay shift due to the influence of the fundus movement. The (minimum)time from the start of capturing one tomogram to the start of capturingthe next tomogram is 12.8 ms. For this reason, if the estimation resultobtained in step S330 indicates that the fundus should move by 250 μmper sec, the relative positional shift between two tomograms is 6.4 μm.The error from the expected interval is about 20%.

To decrease the error, the imaging time is shortened. Assume that theimaging time of the same imaging region is halved (imaging time=0.82sec), and the traversal scan speed is increased. Since the traversalscan speed doubles (936 mm/sec), 128 tomograms each having a 256-pixelwidth can be captured in the imaging region. The time interval betweentomograms changes to 6.4 ms. The relative positional shift between thetomograms decreases to 3.2 μm if the fundus momentum does not change.However, the size per pixel in the traversal scan direction increases to23.44 μm.

The error to calculate the imaging time may be either a value obtainedfrom the instruction acquisition unit 240 or a parameter decided andstored in the data storage unit 250 in advance. In the above-describedembodiment, the imaging time is halved for the sake of convenience.However, based on the tomographic imaging region, the number oftomograms, the fundus momentum, and the designated error, the imagingtime can be simplified by

$\begin{matrix}{t = {E\left( \frac{m}{\left( {s - 1} \right)v} \right)}} & \left\lbrack {{Mathematical}\mspace{14mu} 3} \right\rbrack\end{matrix}$

where t is the imaging time,

E is the error,

$\frac{m}{\left( {s - 1} \right)}$

is the distance between tomograms, and

v is the estimated fundus movement speed

In the above-described method, an example has been explained in whichnot the imaging region but the traversal scan speed is changed (i.e.,the sampling density (sampling period) is decreased). Instead, not thesampling density (sampling period) but the imaging region may bereduced. To halve the error as in the above-described example, theimaging region may be halved (3×2 mm) at the same traversal scan speed.In this case, which one of the tomogram region and the sampling density(sampling period) should be given priority can be either determinedbased on the purpose of examination (e.g., medical examination or closeexamination) obtained from the instruction acquisition unit 240 ordesignated directly by the operator. For example, in medicalexamination, it is preferable to examine a wide range. It is thereforepossible to give priority to the region and decrease the samplingdensity (sampling period).

(Process in Step S1120)

In step S1120, the traversal scan direction can be decided based on thefundus movement direction obtained in step S340. FIG. 12 is a viewshowing the relationship between the fundus movement direction and thetraversal scan direction. Referring to FIG. 12, 1201 represents anexample of the broad image A captured at a high shutter speed; and 1202,an example of the broad image B captured at a low shutter speed. Theinfluence of the small involuntary eye movement defocuses the outline.However, the defocusing manner is the same in all directions so nodirectivity is observed. An example of the broad image B indicated by1203 in FIG. 12 exhibits a strong defocus in the horizontal direction.The broad image B indicated by 1204 in FIG. 12 exhibits a strong defocusin a 45° direction.

When continuously capturing a plurality of tomograms, the relativepositional shift between the tomograms needs to be made as small aspossible. For this purpose, main scan of tomographic imaging is done inthe same direction as the fundus movement direction. Referring to FIG.12, 1206 indicates a traversal scan direction for the movement 1203; and1207, a traversal scan direction for the movement 1204.

In this case, although the start position shift between tomogramsbecomes large, as indicated by 1205 in FIG. 12, the influence of therelative positional shift between the tomograms can be suppressed.However, a mutual information method or a cross-correlation function isalso usable to align the tomograms so as to correct the start positionshift between them. The process in step S340 is executed in theabove-described way.

As described above, according to this embodiment, the traversal scandirection and speed and the imaging range of tomographic imaging aredecided using the analysis result of the image blur amount and directionof a broad fundus image. This enables to obtain a tomogram less affectedby the fundus movement.

Second Embodiment

In the first embodiment, the fundus movement analysis unit 271 executesthe analysis process in step S330 based on the image blur (motion blur)of the broad image B. However, the present invention is not limited tothis. In the second embodiment, a fundus movement is analyzed based onthe optical flow of broad images. The procedure of processing of afundus movement analysis unit 271 will be described below.

The fundus movement analysis unit 271 acquires the region information ofa fundus as the tomographic imaging target from an instructionacquisition unit 240.

The fundus movement analysis unit 271 acquires, from a broad imageacquisition unit 220, a plurality of continuous broad images of theimaging target area at a time interval. In this case, the shutter speedof imaging is set to be high (e.g., seconds). The imaging time intervalis set to 30 images/sec. In this embodiment, an SLO (Scanning LaserOphthalmoscope) may be used as a broad imaging apparatus 2, as describedabove.

In step 330, the optical flow between the broad images is calculated. Todo this, a region of interest (e.g., 128×128 pixels) is defined in thebroad image, and the same pattern is detected from an adjacent frame by,for example, pattern matching. Pattern matching may be performed usingan SSD (Sum of Square Differences).

$\begin{matrix}{{SSD} = {\frac{1}{N}{\sum\left( {{A(x)} - {B(x)}} \right)^{2}}}} & \left\lbrack {{Mathematical}\mspace{14mu} 4} \right\rbrack\end{matrix}$

where A and B are the regions of interest of tomograms that aretemporally adjacent,

x is the pixel position in the region of interest, and

N is the total number of pixels in the region of interest

In an adjacent tomogram, the pattern of the region of interest, that is,a position where the SSD is minimized is searched for. The moving amountand direction of the corresponding region of interest are equivalent tothe momentum and direction of the fundus movement. If the region ofinterest moves by x×y pixels with respect to the adjacent image as aresult of search, an amount l and direction θ of the fundus movement canbe calculated by

$\begin{matrix}{{l = \sqrt{\left( {x^{2} + y^{2}} \right)}}{\theta = {{arc}\; {{tg}\left( \frac{y}{x} \right)}}}} & \left\lbrack {{Mathematical}\mspace{14mu} 5} \right\rbrack\end{matrix}$

Patent reference 5 (Japanese Patent Laid-Open No. 07-107368) describesdetails of motion flow (motion vector) detection between images.

As described above, according to this embodiment, when continuous imagescaptured at a high shutter speed are obtained from the broad imagingapparatus 2, fundus movement information can be acquired by analyzingthe optical flow between the broad images.

Third Embodiment

In the above-described embodiments, the traversal scan direction andspeed and the imaging range of tomographic imaging are set by analyzinga fundus movement. In this embodiment, setting of a more appropriatetomographic imaging start time by fundus movement analysis will bedescribed.

As described above, a small involuntary eye movement contains threemovements (tremor, drift, and flick).

Tremor: a quick movement which always occurs in a small momentum

Drift: a slow movement which always occurs in a large momentum

Flick: a quick movement which occurs at a time interval in a largemomentum

A tremor has a small momentum (momentum change), and its influence ontomographic imaging is relatively small. A drift largely influencestomographic imaging. However, the influence can be reduced by settingthe traversal scan speed and direction. Since a flick occurs to cancelthe momentum (momentum change) of drift, its influence can also bereduced by setting the traversal scan speed and direction. In thisembodiment, tomographic imaging parameter setting to further reduce theinfluence of flicks will be explained. A flick is a fundus movement thatoccurs at a time interval within a measurement time for measuring afundus movement. In this embodiment, the tendency of the time intervalof flicks is detected. Upon detecting a flick, tomographic imaging isstarted. Imaging parameters are set such that tomographic imaging endsbefore the next flick.

To detect a flick, a fundus movement analysis unit 271 analyzes a broadimage acquired by a broad image acquisition unit 220 and calculates theinterval and instant of flicks.

For this purpose, a fundus movement is detected from broad imagescontinuously captured for a time, as described above. When the motionflow to an adjacent broad fundus image has instantaneously become larger(than the average), this is detected as a flick. A plurality of flicksare detected while measuring time, thereby calculating the average timeinterval of flicks.

When the tendency of the time interval has been detected, a tomographicimaging start instruction is sent to the tomographic imaging apparatusvia a tomogram acquisition unit 230 in synchronism with the next flick.The imaging time is set to the average time interval of flicks.

In this embodiment, the average time interval is used as the imagingtime. However, the reference for setting is not limited to this. Aminimum time interval or a time interval distribution may be used as areference for setting. The time interval may be set based on any otherreference such as an operator instruction acquired by an instructionacquisition unit 240.

The temporal probability distribution of flicks of the target eye may beobtained, and a time corresponding to, for example, T25 where no flickoccurs at a probability of 25% may be set, as shown in FIG. 15. Otherthan flicks, when the eyelid of the target eye is included in a broadimage, the target eye is determined to have winked, and the influence ofwink on the tomographic imaging can be reduced in the same way.

As described above, according to this embodiment, a flick or winkinformation is detected by analyzing continuously captured broad images.This enables to reduce the influence of a flick or wink on a tomogram.

Fourth Embodiment

In the above-described embodiments, tomogram parameters are set byanalyzing a fundus movement. However, it is sometimes difficult toappropriately set tomogram parameters based on a fundus movement. Inthis embodiment, an arrangement for outputting a notification, that is,a warning if the conditions of tomogram parameters are not satisfiedwill be described.

A detailed processing procedure to be executed by a control apparatus 1of a tomographic fundus imaging apparatus according to this embodimentwill be explained with reference to FIG. 13. Note that a description ofsteps common to those of the already described processing procedure inFIG. 3 will be omitted.

(Process in Step S1310)

In step S1310, tomogram acquisition parameters set in step S340 areconfirmed to determine whether they are effective parameters thatsatisfy the conditions. As the conditions, imaging instructions obtainedin step S310 are usable. The imaging instructions include an imagingrange.

Upon confirming tomogram acquisition parameters set in step S340 (S1310)and determining that they are effective parameters, the process advancesto step S350 to acquire a tomogram.

On the other hand, if the imaging range decreases to, for example, ½ or¾, the parameters are determined to be ineffective, and the processadvances to step S1320. In step S1320, a display unit 260 displays awarning representing that the tomogram acquisition parameters set instep S340 are not effective. The warning can be done not only bydisplaying a warning message on a monitor 105 of the display unit 260but also by, for example, turning on a warning lamp or making a buzzersound. The criterion of determination is not limited to setting of aparameter to reduce the imaging range to ½ or ¾. Any other condition isusable. As another example of the condition for warning output, when thefundus movement is too large, the imaging time needs to be extremelyshort. In this case, however, the number of samples is too small, and noeffective tomogram can be obtained.

In step S1330, the imaging instructor is required to confirm whether tocontinue imaging.

In step S1330, it is determined based on an input from the imaginginstructor whether to continue imaging. To continue imaging, the processadvances to step S350 to acquire a tomogram. If imaging should notcontinue, the process advances to step 370 to store necessaryinformation, and the overall processing ends.

As described above, according to this embodiment, if it is impossible toobtain an effective tomogram acquisition parameter, a warning is outputto request determination of the imaging instructor. If imaging shouldnot continue, acquisition of ineffective tomograms can be avoided.

Other Embodiments

The present invention is also implemented by executing the followingprocessing. That is, the processing is executed by supplying software(program) for implementing the functions of the above-describedembodiments to a system or apparatus via a network or various kinds ofstorage media and causing the computer (or CPU or MPU) of the system orapparatus to read out and execute the program.

The present invention is not limited to the above embodiments, andvarious changes and modifications can be made within the spirit andscope of the present invention. Therefore, to apprise the public of thescope of the present invention, the following claims are made.

This application claims the benefit of Japanese Patent Application No.2008-271439, filed Oct. 21, 2008, which is hereby incorporated byreference herein in its entirety.

1. An imaging apparatus comprising; a first imaging unit configured toperform imaging of a planar image of a target eye; a second imaging unitconfigured to perform optical coherence tomography by scanning thetarget eye to form a tomogram of the target eye; and a determinationunit configured to determine a parameter to form the tomogram of the eyeused by the second imaging unit, by analyzing a degree of blur in anplanar image of the eye.
 2. The imaging apparatus of claim 1, furthercomprising an analysis unit configured to analyze a degree of blur in anplanar image of the eye, wherein the determination unit determines theparameter based on the result of the analysis.
 3. The imaging apparatusof claim 1, wherein the analsis unit analyzes the planar image to obtainthe degree of blur using point spread function.
 4. The imaging apparatusof claim 1, wherein the first imaging unit performs imaging of aplurality of planar images of the target eye, and the analysis unitanalyzes the planar images to determine the degree of blur in a planarimage of a plurality of the planar images.
 5. The imaging apparatus ofclaim 4, wherein the first imaging unit performs imaging of a firstplanar image to be analyzed, and a second planar image as a referenceimage, and the analysis unit analyzes the degree of blur in the firstplanar image by comparing the first planar image with the second planarimage.
 6. The imaging apparatus of claim 5, wherein the analysis unitminimizes the difference between the first image and the second imagewhich a certain degree of blur are added to by changing the degree ofblur added to the second planar image, and determines the degree of bluradded as the degree of blur in a first planar image.
 7. The imagingapparatus of claim 5, wherein the analysis unit adds a certain degree ofblur to the second planar image and determines the difference betweenthe added image and the first planar image.
 8. The imaging apparatus ofclaim 1, further comprising a warning unit configured to output warninginformation which indicates the determined parameter are out of thespecific range for imaging a tomogram.
 9. The imaging apparatus of claim1, further comprising a control unit configured to control the secondimaging unit according to the determined parameter.
 10. The imagingapparatus of claim 1, wherein the second imaging unit scans a fundus ofthe target eye, receives interference signals and processes the receivedsignals to form the tomogram.
 11. The imaging apparatus of claim 1,wherein the analysis unit determines the degree of blur as a directionand an amount of the movement of the target eye.
 12. The imagingapparatus of claim 1, wherein the first imaging unit is one of a funduscamera unit or a scanning laser ophthalmoscope.
 13. The imagingapparatus of claim 1, wherein the determination unit determines controlunit controls at least one of an imaging range of the imaging unit, ascan speed of the imaging unit within the imaging range, a samplingperiod of imaging of the imaging unit, and an imaging position at whichthe imaging unit starts imaging. as the parameter.
 14. An imagingapparatus comprising; a first imaging unit configured to perform imagingof a planar image of a target eye; a second imaging unit configured toperform optical coherence tomography by scanning the target eye to forma tomogram of the target eye; and an analysis unit configured to analyzea degree of blur in an planar image of the eye; a determination unitconfigured to determine a parameter to form the tomogram of the eye usedby the second imaging unit, based on a result of the analysis by theanalysis unit; and a control unit configured to control the secondimaging unit according to the determined parameter.
 15. A method forcontrolling the imaging system comprising; providing a planar image of atarget eye; analyzing a degree of blur in an planar image of the eye;determining a parameter to form the tomogram of the eye used by thesecond imaging unit, based on a result of the analyzing; and controllinga optical coherence tomography imaging unit included in the imagingsystem to form a tomogram according to the determined parameter.